1. Field
The present invention relates to the field of hydrocarbon recovery from earth formations. More specifically, the present invention relates to the recovery of viscous hydrocarbons such as bitumen. In addition, the present invention relates to the use of excess power supplies for the generation of steam (or hot water), which may then be contacted with hydrocarbon-containing earth as part of an oil recovery operation in a subsurface formation, or in a bitumen separation facility associated with a mining operation.
2. Discussion of Technology
This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
A growing demand exists for electricity generated from renewable resources. Such resources include wind and solar energy. Use of such renewable resources for generating electricity releases less emissions than the combustion of fossil fuels.
A drawback to the use of certain renewable resources, such as wind and solar energy, is the inherent fluctuation in the amounts of electrical power they can generate. In this respect, neither wind currents nor solar rays are constant. The fluctuations reflect seasonal, daily, and even hourly variations in wind and solar illumination.
Typically, an electrical power grid connecting one or more power sources to multiple users is ill-suited to accept significant amounts of fluctuating power. The primary reason is that at every instant, the total amount of electricity being fed into a power grid must essentially match the demand from that grid (plus transmission or “line” losses). A power grid does not act as a capacitor, and generally has minimal ability to store electrical power when it is in excess, or to release electrical power when it is in short supply.
One method for dealing with fluctuating power input is to offset such fluctuations with a separate power source that can be rapidly turned on, turned off, or adjusted. Such separate power sources may include hydroelectric power generators or gas turbines. However, having such generators and turbines tends to be economically inefficient since significant amounts of costly power generation equipment may sit idle at times or at least be run well below capacity. Another way to deal with fluctuating power is to store energy when it is in excess, and release energy when it is in short supply. Various methods have been proposed for large-scale energy storage. These include, for example, water-lifting, air compression, massive batteries, and hydrogen generation and storage. However, such methods tend to have relatively limited storage capacities and can be costly to implement.
Normally unrelated to the problem of power-matching is the production of viscous hydrocarbons. The term “hydrocarbons” generally refers to any organic material with molecular structures containing carbon bonded to hydrogen. Viscous hydrocarbons refers to those hydrocarbons that reside in a highly viscous or even solid (non-fluid) form. Such hydrocarbons may generally be referred to as “heavy hydrocarbons” and “solid hydrocarbons,” respectively.
Heavy hydrocarbons include hydrocarbons that are highly viscous at ambient conditions (15°-25° C. and 1 atm pressure). These include bitumen, asphalt, natural mineral waxes, and so-called heavy oil. “Solid hydrocarbons” refers to any hydrocarbon material that is found naturally in substantially solid form at formation conditions. Examples include kerogen, coal, shungites, and asphaltites.
The viscosity of heavy hydrocarbons is generally greater than about 100 centipoise at 15° C. Bitumen and heavy oil are sometimes together referred to as viscous oils. Heavy hydrocarbons may also be classified by API gravity, and generally have an API gravity below about 20 degrees. Heavy oil, for example, generally has an API gravity of about 10 to 20 degrees, whereas tar generally has an API gravity below about 10 degrees.
The terms “bitumen” and “tar” are sometimes used interchangeably. Both materials are highly viscous, black, and sticky substances. However, the naturally occurring tar in subsurface formations is technically bitumen. Bitumen is a non-crystalline, highly viscous hydrocarbon material that is substantially soluble in carbon disulfide. Bitumen includes highly condensed polycyclic aromatic hydrocarbons, and is commonly used for paving roads.
Viscous oil deposits are located in various regions of the world. For example, viscous oils have been found in abundance in the Milne Point Field on the North Slope of Alaska. Viscous hydrocarbons also exist in the Jobo region of Venezuela, and have been found in the Edna and Sisquoc regions in California. In addition, extensive formations of oil sands exist in northern Alberta, Canada. These formations are sometimes referred to as “tar sands,” though they technically contain bitumen.
The Athabasca oil sands deposit in northern Alberta is one of the largest viscous oil deposits in the world. There are also sizable oil sands deposits on Melville Island in the Canadian Arctic, and two smaller deposits in northern Alberta near Cold Lake and Peace River. The oil sands contain substantial amounts of bitumen.
The extraction of viscous oil deposits is oftentimes carried out through the injection of or contacting with heated fluids. For example, heavy oil deposits in California are produced by injecting hot water or steam. Heated fluids mobilize heavy hydrocarbons and separate them from the rock matrix in situ. The heated fluid may be steam. Alternatively, the heated fluid may be a solvent vapor or a steam-solvent mixture. For mined bitumen deposits, the mined oil containing earth may be contacted with heated water and/or solvent to encourage separation of bitumen from the earth solids.
The process of heating water and solvent for subsurface operations requires a great deal of energy. In this respect, large quantities of fluid must be heated to very high temperatures in order to mobilize viscous hydrocarbons. Therefore, a need exists for improved methods of stabilizing electrical power grids tied to fluctuating power sources, such as wind and solar power. Moreover, a need exists to obtain economic advantage from fluctuating power sources by using excess power from an electrical power plant to support the production of viscous hydrocarbons, such as in an enhanced oil recovery operation or in a bitumen separation facility.